Re: Mersenne: Re: double-check mismatches

[Kevin Sexton]

As far as I know overclocking is not done to the extent that it was in 
the past, when with proper cooling  some processors would operate at a 
signifigant percentage increase in speed. New processors operate in the 
microwave range when you look at their frequencies. You can imagine 
wierd things that may happen in a chip when you go from 3.2 Ghz to 4.2, 
strange things with induction and capacitance of the traces, a signal on 
one trace jumping to another as an RF signal, it just doesn't seem to me 
to be worth the effort to push a chip beyond it's rated speed anymore. 
Also the bottleneck is not so much the processor, but memory, chipset 
and graphics card have a large impact on how fast that game plays. It is 
now more work, for less benefit to overclock.

Brian J. Beesley wrote:

On Friday 16 January 2004 06:10, Max wrote:
 

It would be also interesting to learn how often the first run is bad, and
how often is the second?
   

Yes - I don't think this information is readily available, though sometimes 
you can infer the order of completion from the program version number.

To do the job properly either the "bad" database would need an extra field 
(date of submission) or a complete set of "cleared.txt" files would be 
required - and this would miss any results submitted manually.
 

It seems to me that first run should be bad more often than the second. Is
that true? My reasoning is that first run is usually done on modern
(fast/overclocked/unstable/etc) hardware while the second one is done on
the old/slow but more stable/trusted hardware.
   

Interesting theory - but surely the error rate would be expected to be 
proportional to the run length, which would tend to make fast hardware appear 
to be relatively more reliable - conversely smaller / lower power components 
(required to achieve high speed) would be more subject to quantum tunnelling 
errors. For those who think in terms of cosmic rays, this means a less 
energetic particle hit will be enough to flip the state of a bit.

In any case the exponents ~10,000,000 which are being double checked now were 
originally tested on "leading edge" hardware about 4 years ago, when 
overclocking was by no means unknown but was often done without the sort of 
sophisticated cooling which is readily available these days.

Regards
Brian Beesley
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